This invention relates to a process for the preparation of conjugated linoleic acid (CLA). The process overcomes the high input costs of alkali and oil by using soapstock, soap and other vegetable oil refining by-products as the source of linoleate moieties. Surprisingly, refining wastes enriched in soaps may be converted to CLA with the addition of substoichiometric amounts of alkali. The reaction is unique in that it allows the utilization of an inexpensive by-product of vegetable oil refining to produce CLA.
Conjugated linoleic acid is the trivial name given to a series of eighteen carbon diene fatty acids with conjugated double bonds. Applications of conjugated linoleic acids vary from treatment of medical conditions such as anorexia (U.S. Pat. No. 5,430,066) and low immunity (U.S. Pat. No. 5,674,901) to applications in the field of dietetics where CLA has been reported to reduce body fat (U.S. Pat. No. 5,554,646) and to inclusion in cosmetic formulae (U.S. Pat. No. 4,393,043).
CLA shows similar activity in veterinary applications. In addition, CLA has proven effective in reducing valgus and varus deformity in poultry (U.S. Pat. No. 5,760,083), and attenuating allergic responses (U.S. Pat. No. 5,585,400). CLA has also been reported to increase feed conversion efficiency in animals (U.S. Pat. No. 5,428,072). CLA-containing bait can reduce the fertility of scavenger bird species such as crows and magpies (U.S. Pat. No. 5,504,114).
Industrial applications for CLA also exist where it is used as a lubricant constituent (U.S. Pat. No. 4,376,711). CLA synthesis can be used as a means to chemically modify linoleic acid so that it is readily reactive to Diels-Alder reagents (U.S. Pat. No. 5,053,534). In one method linoleic acid was removed from oleic acid by first conjugation then reaction with maleic anhydride followed by distillation (U.S. Pat. No. 5,194,640).
Conjugated linoleic acid occurs naturally in ruminant depot fats. The predominant form of CLA in ruminant fat is the cis,trans-9,11-octadecadienoic acid which is synthesized from linoleic acid in the rumen by micro-organisms like Butryvibrio fibrisolvens. The level of CLA found in ruminant fat is in part a function of dietary cis,cis-9,12-octadecadienoic acid and increase marginally in ruminant milk and depot fat by feeding linoleic acid (U.S. Pat. No. 5,770,247).
CLA may also be prepared by any of several analytical and preparative methods. Pariza and Ha pasteurized a mixture of butter oil and whey protein at 85xc2x0 C. for 5 minutes and noted elevated levels of CLA in the oil (U.S. Pat. No. 5,070,104). CLA produced by this mechanism is predominantly a mixture of cis,trans-9,11-octadecadienoic acid and trans,cis-10,12-octadecadienoic acid.
CLA has also been produced by the reaction of soaps with strong alkali bases in molten soaps, alcohol, and ethylene glycol monomethyl ether (U.S. Pat. No. 2,389,260, U.S. Pat. No. 2,242,230 and U.S. Pat. No. 2,343,644). These reactions are inefficient as they require the multiple steps of formation of the fatty acid followed by production of soap from the fatty acids, and subsequently increasing the temperature to isomerize the linoleic soap. The CLA product is generated by acidification with a strong acid (sulfuric or hydrochloric acid) and repeatedly washing the product with brine or CaCl2.
CLA has been synthesized from fatty acids using SO2 in the presence of a substoichiometric amount of soap forming base (U.S. Pat. No. 4,381,264). The reaction with this catalyst produced predominantly the all trans configuration of CLA.
Efficient synthesis of cis,trans-9,11-octadecadienoic from ricinoleic acid has been achieved (U.S. Pat. No. 5,892,074). This synthesis, although efficient, uses expensive elimination reagents such as 1,8-diazobicyclo-(5,4,0)-undecene. For most applications the cost of the elimination reagent increases the production cost beyond the level at which commercial production of CLA is economically viable.
Water may be used in place of alcohols in the production of CLA by alkali isomerization of soaps (U.S. Pat. No. 2,350,583, U.S. Pat. No. 4,164,505). When water is used for this reaction it is necessary to perform the reaction in a pressure vessel whether in a batch (U.S. Pat. No. 2,350,583) or continuous mode of operation (U.S. Pat. No. 4,164,505). The process for synthesis of CLA from soaps dissolved in water still requires a complex series of reaction steps. Bradley and Richardson (Industrial and Engineering Chemistry February 1942 vol 34 no2 237-242) were able to produce CLA directly from soybean triglycerides by mixing sodium hydroxide, water and oil in a pressure vessel. Their method eliminated the need to synthesize fatty acids and then form soaps prior to the isomerization reaction. However, they reported that they were only able to produce an oil with up to 40% CLA. Quantitative conversion of the linoleic acid in soybean oil to CLA would have produced a fatty acid mixture with approximately 54% CLA.
Commercial conjugated linoleic acid often contains a mixture of positional isomers that may include trans,cis-8,10-octadecadienoic acid, cis,trans-9,11-octadecadienoic acid, trans,cis-10,12-octadecadienoic acid, and cis,trans-11,13-octadecadienoic acid (Christie, W. W., G. Dobson, and F. D. Gunstone, (1997) Isomers in commercial samples of conjugated linoleic acid. J. Am. Oil Chem. Soc. 74,11,1231).
One object of this invention is to provide a method of production of CLA using soapstock and other by-products from the refining of vegetable oils that are rich in linoleic acid.
By one aspect of this invention there is provided a process for producing a salt of conjugated linoleic acid comprising; refining a linoleic acid rich vegetable oil with a solution selected from the group consisting of water, glycerol and glycol solutions containing an alkali so as to produce a soapstock containing salts of linoleic acid; reacting said soapstock with a substoichiometric addition of an alkali at a temperature of at least 170xc2x0 C.; and liberating said salt of conjugated linoleic acid by addition of at least one of the group consisting of an acid, a monovalent salt solution and a polyvalent salt solution.